1. Field of the Invention
This invention relates to a heat pipe and, in particular, a heat pipe which carries an evaporable working fluid and which includes a wick.
2. Description of the Prior Art
In a known heat pipe of the above type, the wick is in the form of a hollow, cylindrical member having an outer surface which rests against the inside diameter of the wall of the pipe and an inner surface which is adjacent a vapor space extending through the central portion of the interior of the pipe. Additionally, the pipe is evacuated and filled with a small amount of an evaporable working fluid, such as, e.g., water or alcohol. In use, one end of the pipe is brought into contact with a heat source from which heat is to be removed and, simultaneously, therewith the opposite end of the pipe is cooled. At the end adjacent the heat source an evaporation section or region is created where the working fluid in the wick evaporates and the resultant vapor enters into the vapor space. In turn, at the other end of the pipe a condensation section is formed. Since the vapor pressure in the region of the evaporation section is higher than in the region of the condensation section, the vapor molecules move through the vapor space from the evaporation section toward the condensation section. In the latter section the evaporated working fluid is condensed and is drawn back into the wick through capillary action along the wick surface adjacent the vapor space. The wick then carries the fluid back to the evaporation section where the cycle of operation is again repeated.
In the above known heat pipe, the wick is typically comprised of netting, felt or sintered layers, which have a homogeneous structure with substantially uniform pore size over the entire layer thickness. As a result of employing a wick with a uniform pore size, one is faced with having to select a single pore size which best satisfies two contradictory requirements. Small pores, on the one hand, permit large capillary pressure differences and, therefore, good absorption of the condensed vapor back into the wick. On the other hand, small pores offer increased resistance to the reflow of the condensed working fluid back through the wick, which counteracts the good absorption capacity. Large pores have just the opposite effect, i.e., offer low resistance to reflow of the condensed working fluid, but provide the small capillary pressure differences. In this known heat pipe, therefore, selection of the wick pore size necessarily involves a compromise between achieving maximum reflow and maximum capillary pressure differences.
In another known heat pipe an attempt has been made to overcome the latter disadvantage by providing separate, free canals, so-called "arteries" for the backward flow of the working fluid. For working fluids which boil quickly such as, for example, water or alcohol, these so-called "artery heat pipes" have not proved satisfactory, as the backward flow of the working fluid in the free canals is blocked by the formation of steam bubbles.
It is an object of the present invention to provide a heat pipe having an increased heat removing capacity.